“A long time ago the food industry looked at the price of beef and said, ‘If we want to put that in ramen noodles or gravy, we can’t be extracting flavor and throwing away the beef—it’s too expensive,” Gary ReinecciusTeaLaiumens/Wikimedia Commons
, a food chemist specializing in flavor research, told Eater. “So they needed to find a way to make the flavors that didn’t start with meat products.”

How do they do that, exactly?

“Food scientists identified the amino acids found in beef, added some very common sugars—starch hydrolysate—put it in a pot, added some citric acid to drop the pH, controlled moisture content, and heated it to the same temperature as meat,” Reineccius explained. “Then…*poof* we have meat flavor.”

McDonald’s creates its fries by starting with a base of hydrolyzed wheat and hydrolyzed milk, as the website notes. This creates processed free glutamic acid, otherwise known as monosodium glutamate or MSG.

Through the past several decades, scientific studies have indicated that some people react poorly to MSG, and for a time, researchers believed that the substance caused headaches, nausea, and other symptoms. However, a review in the Journal of the American Academy of Nurse Practitioners showed that there’s “no consistent clinical data” to support those claims.

That’s good news, and McDonald’s lovers just breathed a sigh of relief.

Unfortunately, we’ve also got a bit of bad news. Some studies show that certain umami tastes can make people hungrier. MSG might influence metabolism and “stimulate the orosensory receptors,” potentially causing a person to overeat.

Can we blame MSG for making McDonald’s fries so addictive? Not entirely. They’re also fried in fat and coated in salt, and anything salty and fatty will taste pretty good. Still, MSG might play a role, and regardless, dieters should beware.

A small fry packs in 230 calories with 29 grams of carbs and 11 grams of fat. Spring for a large, and you’re putting away 510 calories—more calories than what you’d find in a McDonald’s cheeseburger.

In other words: No, we don’t want fries with that, but thanks for asking.